/**
 * Copyright 2006 gworks.com.au
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License. (http://www.apache.org/licenses/LICENSE-2.0)
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed 
 * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for 
 * the specific language governing permissions and limitations under the License.
 *
 * <dhamma-message src="Atisha (11th century Tibetan Buddhist master)">
 *  The greatest achievement is selflessness. The greatest worth is self-mastery.
 *  The greatest quality is seeking to serve others. The greatest precept is continual awareness.
 *  The greatest medicine is the emptiness of everything. The greatest action is not conforming with the worlds ways.
 *  The greatest magic is transmuting the passions. The greatest generosity is non-attachment.
 *  The greatest goodness is a peaceful mind. The greatest patience is humility.
 *  The greatest effort is not concerned with results. The greatest meditation is a mind that lets go.
 *  The greatest wisdom is seeing through appearances. 
 * </dhamma-message>
 * 
 * @author Ashin Wimalajeewa (ash)
 */
package org.javaongems.rico.client;

import com.google.gwt.user.client.Element;

public class OpacityEffect extends ElementEffect {
	private float opacity, orig;
	
	public OpacityEffect(Element elem, float op) {
		super(elem);
		opacity = op;
	}
	
	public void reverse() {
		super.reverse();
		float tmp = orig;
		orig = opacity;
		opacity = tmp;
	}
	
	public void start() {
		super.start();
		orig = getElementOpacity(element);
	}
	
	public void transition(int step, int remainingSteps, int stepDuration) {
		super.transition(step, remainingSteps, stepDuration);
	    float currentOpacity = getElementOpacity(element);
	    float delta = (opacity - currentOpacity)/remainingSteps;
	    changeOpacityBy(delta);
	}
	
	private void changeOpacityBy(float delta) {
	      float currentOpacity = getElementOpacity(element);
	      float newOpacity = Math.max(0, Math.min(currentOpacity+delta, 1));
	      setElementOpacity(element, newOpacity);
	}
	
	native public static void setElementOpacity(Element e, float o) /*-{
	      e.ricoOpacity = o;
	      e.style.filter = "alpha(opacity:"+Math.round(o*100)+")";
	      e.style.opacity = o;;
	}-*/;
	
	native public static float getElementOpacity(Element e) /*-{
    	if (e.ricoOpacity == undefined) {
      		var opacity;
            if (e.currentStyle)
         		opacity = e.currentStyle['opacity'];
      		else
         		opacity = document.defaultView.getComputedStyle(e, null).getPropertyValue('opacity');
         	e.ricoOpacity = opacity != undefined ? opacity : 1.0;
      	}
      	return parseFloat(e.ricoOpacity);
	}-*/;
}
